1. Field of the Invention
The present invention relates to a surface texture measuring instrument for measuring a surface roughness, waviness, and profile of a workpiece.
2. Description of the Related Art
A surface texture measuring instrument has a detector having a stylus at a distal end thereof, the stylus being moved along a measurement surface to detect displacement of the stylus as a measurement data.
The detector used in the surface texture measuring instrument has an elongated arm member rotatably attached inside an approximately cylindrical casing. A stylus arm having a stylus is provided at the distal end of the arm member. Displacement of the stylus is detected by a detecting unit provided to the arm member.
Conventionally, in order to rotatably support the arm member inside the casing, a pivot has been fixed to a rotation center of the arm member and a bottomed cylindrical bearing for engaging a pointed end of the pivot in a bottom bearing hole is fixed to the casing (Japanese Patent Publication Laid-Open Publication No. Hei 11-248404).
Further, in another conventional arrangement, a spring for pre-loading the arm member is provided in the casing to press the stylus toward the measurement surface (Japanese Patent Publication Laid-Open Publication No. Hei 11-190605).
Since a stylus arm of a different type has to be used in some measurement process, the stylus arm is capable of being plugged in and out of a recess formed at an end of the arm member.
Generally, the surface texture measuring instrument is used for conducting measurement with a skid (referred to xe2x80x9cskid measurementxe2x80x9d hereinafter) and skidless measurement without using a skid.
Accordingly, the skid is attached to the casing to cover the stylus in the detector of the surface texture measuring instrument. The skid is attached to the casing by a bolt, so that the skid is capable of being attached and detached relative to the detector body.
The skid measurement is used in order to remove a waviness component and to detect only roughness component data when the measurement surface has both waviness and roughness. During the measurement, the detector is moved while both the stylus and the skid are in contact with the measurement surface.
The skidless measurement where the skid is detached from the detector body is used for measuring a cross-sectional profile and straightness of the workpiece by detecting all of the concave-convex data of the measurement surface including waviness, etc. During the skidless measurement, the detector is moved while only the stylus is in contact with the measurement surface.
In the surface texture measuring machine, especially in the surface roughness tester, it has been desired that a workpiece be measured at a minute measuring force of 0.75 mN. However, in the conventional arrangement, the micro measuring pressure has been difficult to achieve on account of measuring orientation in accordance with measuring condition and problems caused in exchanging the stylus arm.
Specifically, though the above conventional art disclosed in Japanese Patent Publication Laid-Open No. Hei 11-248404 can work at the micro measuring pressure, since a force is applied between a pointed end of the pivot fixed to the arm member and the bearing hole of the bearing in plugging the stylus arm in and out, durability of the bearing is inferior. Further, when a great plugging force is applied in exchanging the stylus arm, the bearing cannot sustain the plugging force, and an independent special mechanism is additionally required.
A ball bearing is used for improving durability of the bearing.
For using the ball bearing, in a detector for the surface texture measuring instrument, a pivot may be respectively fixed on both sides of the rotation center of the arm member, and the ball bearing respectively engaging to the pivot may be disposed in the casing.
In order to sufficiently support the pivot by the mutually opposing ball bearings, it is preferable that one of the ball bearings may be fixed to the casing and the other ball bearing may be pressed by one end of a leaf-spring with the other end being fixed to the casing.
However, when the ball bearing is merely pressed by the end of the leaf-spring, the ball bearing abutting the leaf-spring may be shifted by plugging the stylus arm in and out, so that the measuring pressure may be fluctuated in accordance with the position shift of the ball bearing.
Especially, in the detector of the surface texture measuring instrument for measurement with micro measuring pressure, the stylus arm can be fixed and unable to turn on account of the change in the measuring pressure caused in accordance with position shift of the ball bearing.
Further, since the pressing force against the measurement surface of the stylus is determined by the spring force of a spring for pre-loading the arm member in the conventional arrangement of Japanese Patent Publication Laid-Open Publication No. Hei 11-190605, minute change in measuring pressure required for exchanging the stylus arm cannot be sufficiently conducted.
Further, in the conventional arrangements, the skid measurement and the skidless measurement are conducted by attaching and detaching the skid relative to the casing of the detector. However, in both cases, since a straightness correction function has to be switched on and off and a surface roughness calculation and a surface profile calculation have to be switched in accordance with the presence of the skid, troublesome operation has been required and error is likely to occurr.
Further, in order to conduct recalculation after the data outputted by the detector is stored, it has been difficult to identify whether the data was obtained by the skid measurement or the skidless measurement.
An object of the present invention is to provide a detector for a surface texture measuring instrument capable of highly accurate measurement even with a micro measuring force in accordance with a measuring condition.
A detector for a surface a texture measuring instrument according to the present invention has: an arm member detachably attached with a stylus arm having a stylus at a distal end thereof; and a casing rotatably holding the arm member. The detector being characterized in that pivots project from both sides of a rotation center of the arm member, that a first ball bearing engaged to a distal end of one of the pivots is fixed to the casing, and that a second ball bearing engaged to a distal end of the other one of pivots is attached to the casing through a leaf-spring, the leaf-spring pre-loading the second bearing to the pivot and having one end fixed to the casing and the other end fixed to the ball bearing.
In the present invention, when the detector is moved while the stylus is in contact with the measurement surface, the stylus is displaced along an irregular surface on the measurement surface, the displacement being transmitted as a rotary (seesawing) movement of the stylus arm and the arm member.
Pivots are respectively attached to a rotation a center on both sides of the arm member, the pivots being supported by the ball bearings.
In the present invention, rotary torque can be decreased by using the ball bearing. Further, the stylus can be exchanged by widely supporting the shaft, thus minimizing hysteresis and enabling measurement with a low measuring force.
Since one of the ball bearings is fixed to the leaf-spring and is movable while following the leaf-spring, highly accurate slide movement of the pivot ball bearing is not required, thus reducing production cost.
Even when a force is applied to the bearing in pulling out and inserting the stylus arm, since the ball bearing does not shift relative to the leaf-spring, fluctuation of the rotary torque can be restrained, thus not fluctuating measuring pressure thereafter.
A detector for a surface texture measuring instrument according to the present invention has: an arm member detachably attached with a stylus arm having a stylus at a distal end thereof; and a casing rotatably holding the arm member, the detector being characterized in that a balance weight for balancing weight of the stylus arm and the arm member at a rotation center of the arm member is attached to at least one of the stylus arm and the arm member, the balance weight being movable in an axial direction.
In the present invention, when the stylus arm is exchanged into a different type, the weight center of the arm member and the stylus arm can be shifted. In this case, the measuring pressure can be minutely adjusted by axially sliding the balance weight.
In the above arrangement, the balance weight may preferably have a weight body disposed on an end of the arm member and a screw portion having a base end fixed to the weight body and being screwed to a female screw extending in the longitudinal direction of the arm member.
According to the above arrangement, since the balance weight includes the weight body and the screw portion, the balance weight can be easily slid by rotating the weight body to adjust screwing amount of the screw portion.
A detector for a surface texture measuring instrument according to the present invention has: an arm member detachably attached with a stylus arm having a stylus at a distal end thereof; a casing rotatably holding the arm member; and a skid detachably attached to the casing with a distal end disposed around the stylus, the detector being characterized in having a detecting switch for detecting whether the skid is attached to the casing or not.
In the present invention, whether the skid is attached or not can be detected by the detecting switch, so that switching on and off the straightness correction function and switching between a surface roughness calculation and a surface profile calculation are automatically possible, thereby facilitating operation thereof and avoiding error.
Further, when the data outputted by the detector is stored, the output signal outputted by the detecting switch is also stored, so that it can be facilitated to identify whether certain data is collected by the skid measurement or the skidless measurement. And switching on and off the straightness correction function and switching between the surface roughness calculation and the surface profile calculation are automatically possible during re-calculation, thereby facilitating operation thereof and avoiding error.
An example of the detecting switch is a limit switch, a pressure-sensitivity switch using a piezoelectric device.
When the limit switch is used as the detecting switch, the structure of the detecting switch can be simplified.